Numerous chlorofluorocarbons (CFCs) are known in the art to have industrial and household applications including uses as refrigerants, solvents and blowing applications, however, they are believed to be deleterious to the earth's protective ozone layer. Because of the potential danger to atmospheric ozone by CFCs, it is desired to develop substitutes which function in substantially the same way but which are essentially not ozone depleting. Several such replacement materials include 1-chloro-1,2,2,2-tetrafluoroethane (HCFC-124), 1-chloro-1,1,2,2,-tetrafluorochloroethane (HCFC-124a) and pentafluoroethane (HFC-125). It is expected that the demand for these materials will increase dramatically in the future and hence commercially viable processes for the preparation of these materials are advantageous. Many processes for the production of HCFC's and HFC's are known in the art. Many of these use catalysts which are not very selective and in addition to producing the desired materials, produce a wide variety of undesired by-products. Some of the catalysts have a very short life span and hence they are impractical for commercial application. In addition, the operating conditions described in the art made commercial production impractical. The following are typical of prior art methods.
U.S. Pat. No. 3,258,500 describes a single stage process for the production of HCFC-124 and HFC-125 by reacting tetrachloroethylene with anhydrous hydrogen fluoride in the presence of a fluorination catalyst. The catalyst may be activated anhydrous chromium oxide on alumina. This process has an exceedingly low selectivity and yield. U.S. Pat. No. 4,843,181 describes a gas phase single stage process which reacts tetrachloroethylene with hydrogen fluoride in the presence of chromium oxide. In order to obtain the desired product, an extremely long contact time is required between the catalyst and the reactants. U.S. Pat. No. 4,967,023 discloses a single stage process which hydrofluorinates perchloroethylene with a chromia on AlF.sub.3 catalyst. A low conversion of reactants is noticed. Similar single stage processes and low yields are described in U.S. Pat. No. 4,766,260. The gas phase, single stage conversion of perchloroethylene to other HCFC's is shown in U.S. Pat. No. 5,091,601.
U.S. Pat. No. 5,155,082 describes a partially fluorinated aluminum/chromium oxide catalyst for the hydrofluorination of a halogenated aliphatic hydrocarbon to produce a chlorofluorocarbon, hydrochlorofluorocarbon or hydrofluorocarbon. According to this patent, when HCFC-124 is the desired hydrofluorocarbon the preferred starting material is HCFC-123 or HCFC-123a. HCFC-123 or HCFC-123a, in turn, preferably is produced from perchloroethylene as the starting material. This entails a two reactor system. Although it mentions that many of the by-products formed during the course of the fluorination reactions can be recycled for the production of additional hydrochlorofluorocarbons and HCFC-124 is specifically listed as one of the byproducts of the production of HCFC-123 from perchloroethylene, there is no disclosure of any process for obtaining HCFC-124, HCFC-124a or HFC-125 as the major products from perchloroethylene from a single step reaction. Prior to this invention the production of HCFC-124 involved two separate reactive stages. First perchloroethylene was hydrofluorinated to produce HCFC-123 and HCFC-123a and then in a separate reactive system, the HCFC-123 and HCFC-123a were hydrofluorinated to produce HCFC-124. Now, due to this invention, there is no longer a need for two separate reactive stages and all the additional equipment which such a two stage system would require. The process of the invention produces HCFC-124 as the major product, as well as HCFC-124a and HFC-125 from perchloroethylene in a single reactive stage. Consequently, one significant advantage is that less equipment is required, particularly since only one reactor vessel is necessary.